Reliability Evaluation of Large-Area Sintered Direct Bonded Aluminum Substrates for Medium-Voltage Power Modules

Abstract

This thesis investigates techniques for prototyping and evaluation of medium voltage (MV) power module packages. Specific focus will be given to the utilization of silver sintering as a bonding method for high temperature, high density power modules. Nano-silver paste and preform will be examined in detail as enabling technologies for a new generation of power electronics. To accomplish this task, analysis and characterization of the metal-ceramic substrate and its structure is performed. First, finite element models are created to evaluate the fatigue behavior of the large area bonds in the substrate structure. Prototypes of these multi-layer substrates have also been fabricated and will be subjected to thermal cycling tests for experimental verification of the efficacy of their sintered silver bonds. Stacked direct-bonded aluminum (DBA) substrates have been found to withstand up to 1000 thermal cycles of –40 °C to 200 °C when attached with low pressure-assisted silver sintering. The thermal performance of 10 kV SiC power module utilizing multi-layer DBA substrates bonded with a large-area, low pressure-assisted sintered silver bond will also be examined to ensure the sintered bond is viable for the harsh operating conditions of MV modules. A junction-to-case thermal resistance of 0.142 °C/W is measured on a module prototype utilizing stacked DBA substrates. Finally, analysis of a double-sided cooling scheme enabled by large area sintering is simulated and prototyped to demonstrate a 6.5 kV package for a MV power device. Residual stress failures induced by a highly rigid structure have been examined and mitigated through implementation of a 5 MPa pressure-assisted, double-sided silver sintering approach.